A possible mechanism for the efflux of unbound cytoplasmic dopamine is the reversal of carrier mediated transport of dopamine. Efflux of dopamine was measured from rat corpus striatum in vitro and the results indicate that amphetamine accelerates the efflux of dopamine by utilization of the carrier transport system while fenfluramine enters by passive diffusion and does not result in increased access of dopamine to the carrier since the carrier remains on the outside of the membrane. The neuronal uptake of biogenic amines and the activation of postsynaptic receptors may be dependent upon the lipid environment in which these processes take place. Pregnant rats were fed semisynthetic diets enriched in either saturated fats with coconut oil or polyunsaturated fats with sunflower oil in an attempt to alter membrane lipids of atria taken from the developing pups. The results suggest that membrane fatty acids can be changed in developing animals and that these changes are associated with changes in membrane fluidity, neuronal uptake of transmitters, beta-receptor activation, adenylate cyclase activity, atrial rate and locomotor activity.